Wireless headsets and other portable communications devices are often battery powered such that a user can use the wireless headset or other such device without being directly connected to larger power source such as an a/c outlet or automobile battery. This allows wireless headset users flexibility and convenience to move about without being tied to a power cord. Wireless headset batteries are generally rechargeable so that the batteries can be recharged and need not be discarded after use.
Recharging of device batteries has generally achieved by a wired connection. In the prior art, devices employing rechargeable batteries typically have charging contacts so that charging current power can be supplied to recharge the batteries without removing the batteries from the device. In one typical setup, the portable device is inserted into a base charger which has spring loaded contacts that correspond to and couple with the contacts on the portable device. For example, such a setup is used with remote handset phones used in the home. The base charger is connected to a power source, and supplies charging current through the coupled contacts to recharge the batteries located within the device. Spring-loaded surface wiping contacts are generally used with charging bases. This is a convenience feature as users can simply drop the portable device into a cradle without fumbling with a plug. Surface contacts can be placed on the side of a taper form headset or other portable rechargeable device, making docking into a cradle much easier than a plug.
However, use of surface contacts and a charging base station with a headset presents problems due to the smaller physical size and design of headsets. Exposed metal contacts on headsets also risk contamination by oils and moisture from the skin of the wearer. This may cause corrosion and hence poor contact with the base station. Contamination also may cause an electrical leakage path that may cause power loss from the battery and electrolytic activity. Exposed metal contacts may also result in an allergic reaction to the user if in prolonged contact with the user's skin. During the rechargeable device docking process, the formed ends of the base station charging contacts often come into contact with the plastic housing of the rechargeable device and can scratch the housing and pick up contamination which can cause intermittent electrical contact. One potential solution is to cut the rechargeable device housing away to fully expose the rechargeable device stationary contacts so that the spring loaded contacts of the base station never touched the plastic housing during docking. However, this solution may compromise the rechargeable device industrial design, aesthetics, and possibly weaken the rechargeable device structural integrity.
Furthermore, the headset or other rechargeable device may not be firmly detented with the charging base, which may also cause intermittent electrical contact. One potential solution to the weak coupling between the portable rechargeable device and charging base to dish the stationary contacts in the rechargeable device so that the rechargeable device detents when the ends of the spring loaded base station contacts press into the depressions in the rechargeable device contacts. However, this solution compromises the industrial design of the rechargeable device, and in addition the detent force is less than robust.
As electronic items become smaller and the regulatory requirements become more stringent, the charging port becomes more noticeable as a relatively large unattractive feature of the housing, as an ESD weakness, as a relatively unreliable element in the system.
In the prior art, contactless battery chargers have also been utilized. The use of inductive coupling used for contactless power transfer between electrical items is described in the prior art. The magnetic field generated by one coil is made to couple closely with that of a second coil. Changes in the field induce a voltage in the second coil hence power transfer is possible. Inductive charging is discussed in U.S. Pat. No. 3,840,795, Electric Toothbrush, U.S. Pat. No. 3,938,018, Charger for electronic items, U.S. Pat. No. 4,873,677, Rechargeable watch. Basic inductive charging components are available from companies such as Panasonic and TDK.
FIG. 1 illustrates a typical prior art arrangement to ensure close coupling as disclosed in U.S. Pat. No. 5,600,225. In this arrangement, mechanical coupling between the charger and radiotelephone is required. The charger 1 for supplying power for charging to the radiotelephone is installed within a base case 101. A depression 102 into which the radiotelephone may be inserted is provided on the upper surface of the base case 101, and a primary coil 103 is provided in the base case 101 for producing magnetic flux which runs around the side walls of the depression 102 in a vertical plane. This primary coil 103 is connected to an oscillating circuit for supplying alternating current to the coil.
The radiotelephone 2 is provided with a microphone 202, a console keyboard 203, a display 204, a receiver 205, and an antenna 206 mounted on a slender telephone case 201. Inside the telephone case 201 is a storage battery. The storage battery is connected to a secondary coil 212 by way of an AC-DC conversion circuit.
The base of the telephone case 201 is constructed to allow insertion into the depression 102 provided in the base case 101, and in this way the radiotelephone 2 may be placed on the charger 1 in an erect state. The secondary coil 212 is provided within the base portion of the case 201 of the radiotelephone 2.
To operate, the radiotelephone 2 is placed upon the charger 1 when the storage battery is to be charged. At this time, the radiotelephone 2 is held in an erect state by means of insertion of the base portion of the telephone case 201 of the radiotelephone 2 into the depression 102 provided in the base case 101 of the charger 1. An alternating current signal of prescribed frequency generated in this oscillating circuit is supplied to the primary coil 103. As a result, an alternating magnetic field is generated by the primary coil 103 within the depression 102 in the base case 101 of the charger 1. This alternating magnetic field generates an induced electromotive force in the secondary coil 212 arranged in the base portion of the telephone case 201 of the radiotelephone 2.
The prior art device described in reference FIG. 1 as well as other prior art solutions require mechanical coupling between the charger and device to be charged. To make the efficiency of power transfer as high as possible it is necessary to contain the magnetic field so that all, or most, of the field in the first coil is linked to the second. To achieve this it is typically necessary to provide some close mechanical coupling such that there is a form of “plug” and “receptacle” arrangement. Contactless charging has been restricted to ‘mating pairs’ in that the item to be charged and the charger are designed as a pair to achieve a closely controlled mechanical alignment of the coils in each unit, to maximize efficiency. This means that generally these charging methods are custom designed for the appliance due to non standardization of the interface and can require dexterity to use. The costs of the design of the charging system and the additional mechanical design have to be born by the individual product. This has restricted the adoption of contactless charging systems. Removing the requirement for accurate mechanical alignment would allow one charger design to be used across a range of products, allowing the development costs to be born by the range of products and reducing the design time for the introduction of a new product
Furthermore, prior art solutions often allow charging of only one item at a time. Generally, a user has multiple rechargeable devices which require charging power. As a result, the user must transport or use a number of chargers, generally one for each item. As the number of devices used by an individual increases, the multiplicity of chargers becomes problematic.
Thus, improved charging interfaces between charging base stations and rechargeable devices are needed.